Refrigerated tank containers are known, British patent specification No. 2,049,628 discloses a refrigerated tank container which comprises a tank mounted within a framework, the framework comprises end frames joined by longitudinal top and bottom side members. The walls of the framework are completely closed by insulating panels, which define with the tank a cavity for the circulation of a cooling medium for cooling the tank and its contents. A horizontal partition wall extending between the side and end walls of the framework and the tank forms an upper and lower chamber. An inlet and outlet is provided in one end wall to respective chambers, so that a cooling medium can flow from the inlet over the lower portion of the tank in the lower chamber and return in the upper chamber to the outlet.
Such tank containers, in general, are adapted to be connected into an external refrigerating unit or into a refrigerating system of a ship, road tanker or the like, from which the cooling medium is derived.
Such insulating tanks suffer from a considerable number of disadvantages. Firstly, the chambers for the cooling medium are of relatively large volume, and thereby require a considerable volume of cooling medium. Air is generally used as the cooling medium, and thus a refrigerating unit for cooling or chilling the air must be of a relatively large capacity to handle the volume of air required. A further disadvantage of known refrigerated tank containers is that the insulating material can be relatively easily damaged or punctured. By virtue of the fact that the insulating panels are formed in the walls of the framework, they are prone to damage as a result of being knocked against another container or other obstacle or obstruction. A further disadvantage of these known tank containers is that because of the large volume of air required, they tend to be relatively inefficient.
In alternative constructions of refrigerated tank containers, a cooling coil for carrying a liquid refrigerant is wound round the tank. In general, heat insulating material is provided around the cooling coils. These tank containers also suffer from many disadvantages. A particular disadvantage is that the coils carrying the liquid refrigerant can readily easily be damaged, thereby leading to leakage of the refrigerant. This causes the refrigerating unit to be ineffective. Furthermore, it has been found in practice that these tank containers, in general, tend to be relatively inefficient.
Similar difficulties arise in the case of tank containers where the heat transfer medium is used for heating the tank.
There is therefore a need for a tank container which overcomes the problems of known tank containers.